docs: def get_protein_modification_language(identifier_qualified: ParserElement) -> ParserElement:
      """Build a protein modification parser."""
      pmod_identifier = MatchFirst([
          identifier_qualified,
          pmod_default_ns,
          pmod_legacy_ns
      ])
  
      return pmod_tag + nest(
          Group(pmod_identifier)(IDENTIFIER) +
          Optional(
              WCW +
              amino_acid(PMOD_CODE) +
              Optional(
                  WCW +
                  ppc.integer(PMOD_POSITION)
              )
          )
      )